1. Field of the Invention
The present invention relates to a vacuum pump and an abnormality cause estimating method for the vacuum pump, and in particular, to a vacuum pump and an abnormality cause estimating method for the vacuum pump in which, when contact between a rotating body and a stator is sensed, the cause of the contact can be analyzed and properly dealt with.
2. Description of the Related Art
With recent development of electronics, demands for semiconductors such as memories and integrated circuits have been increasing rapidly.
These semiconductors are manufactured by, for example, doping impurities into a semiconductor substrate with a very high purity to provide the semiconductor substrate with electric properties and forming fine circuits on the semiconductor substrate by etching.
These operations need to be performed in a chamber in a high-vacuum state in order to avoid the adverse effect of dust in the air and the like. To exhaust the chamber, a vacuum pump is generally used. In particular, a turbomolecular pump, a type of vacuum pump, is often used due to the small amount of residual gas, easy maintenance and the like.
A manufacturing process for semiconductors includes a large number of steps of allowing various process gases to act on a semiconductor substrate. The turbomolecular pump is used not only to vacuum the chamber but also to exhaust the process gases from the chamber.
The turbomolecular pump has a very small clearance between a stator and a rotating body such as a stator blade that rotates at a high speed. Thus, the rotating body and the stator may contact each other when solid products such as solidified components of the exhaust gas accumulate inside the vacuum pump or when the rotating body is deformed as a result of a creep phenomenon or when wear of a protective bearing progresses.
When the rotating body and the stator are left in contact with each other without maintenance (overhaul), a serious defect may occur.
Thus, maintenance timing is conventionally predicted using a technique described in Japanese Patent No. 3457353. Execution of maintenance is urged at a proper timing to prevent the turbomolecular pump from being made non-reusable.
However, the technique described in Japanese Patent No. 3457353 fails to discriminate an increase in vibration amplitude due to temporally increased unbalance of the rotating body from an increase in vibration amplitude due to the physical contact between the rotating body and the stator.
The technique described in Japanese Patent No. 3457353 also fails to discriminate an increase in vibration amplitude due to mechanical vibration associated with, for example, opening and closing of a vacuum valve to which the pump is connected, or external impact (disturbance) applied to the pump or an apparatus such as a vacuum container to which the pump is connected, from an increase in vibration amplitude due to the physical contact between the rotating body and the stator.
Thus, in WO 2010/007975, the contact between the rotating body and the stator is determined using a vibration sensor such as acceleration pickup which is attached to the stator, in order to accurately sense that the amount of solid products accumulated has become equal to the clearance between the rotating body and the stator. This allows the physical contact between the rotating body and the stator to be accurately detected.
However, the method according to WO 2010/007975 disadvantageously needs to use a band-pass filter and a fixing method using an elastic member in order to enhance reliability of a vibration signal from the stator.
The present invention has been developed in consideration of the above-described conventional problems. An object of the present invention is to provide a vacuum pump and an abnormality cause estimating method for the vacuum pump in which, when contact between a rotating body and a stator is sensed, the cause of the contact can be analyzed and properly dealt with.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.